When implementing Global Load Balancing there is a need to take into account factors that are not apparent when load balancing traffic on a LAN. In particular there is a need to be completely independent of other sites. For this reasons methods such as DNS and HTTP Redirection are attractive for directing clients. This is in direct contrast to local load balancing where methods such as Layer 4 Switching offer superior control of traffic.
The BGP-based algorithm discussed provides a powerful mechanism for determining the network-wise POP for a client. It does not, however, take into account the relative capacity or load of the POPs that traffic is being directed to. The assumption made is that each POP has sufficient capacity to cope with the traffic that it is likely to receive. For this assumption to hold, local load balancing may need to be deployed at each POP. The Super Sparrow implementation has been designed with this in mind and will work with local load balancing technologies such as layer 4 switching technology. In particular, Super Sparrow is designed to work in conjunction with Ultra Monkey which utilises the Linux Virtual Server to effect layer 4 switching.
It is anticipated that in the future the implementation of Super Sparrow will be expanded to allow other, non BGP-based algorithms that may take into account factors such as POP capacity and load. Ideally an algorithm that combines capacity and load information with BGP would provide a very flexible solution.